In internal combustion engines, lubricant oils have been used to lubricate piston rings, cylinder liners, bearings for crank shafts and connecting rods, valve train mechanisms including cams and valve lifters, among other moving members. The lubricant prevents component wear, removes heat, neutralizes and disperses combustion products, prevents rust and corrosion, prevents blow by and prevents sludge formation or other deposits.
As engines produce higher power and are operated under more severe conditions, the lubricating oil's required performance and functionality have dramatically increased. These increased performance demands have resulted in a corresponding increase in the lubricant's expense. Lubricants are being made with increasingly sophisticated and expensive base stocks, including wholly synthetic base stocks. In addition, a wide variety of expensive additives, such as dispersants, detergents, antiwear agents, friction reducing agents, viscosity improvers, extreme pressure modifiers, viscosity thickeners, metal passivators, acid sequestering agents and antioxidants are incorporated into the lubricants to meet functional demands.
Lubricants have been designed to manage several engine condition parameters, such as component wear and corrosion. Lubricating oils have been formulated to ensure the smooth operation of engines under every condition by preventing the wear and seizure of engine parts. Antiwear additives are often combined with carefully selected base stocks to achieve these results. Energy loss at the frictional points of internal combustion engines is also great. For this reason, lubricating oils often include friction modifiers. Similarly, other important engine condition parameters managed by the lubricant include system cooling, deposit formation, corrosion, blow by, foaming, neutralization of combustion by-products, metal passivation and maintaining lubricant film thickness. This list is not meant to be exhaustive and one of ordinary skill in the art recognizes many other important engine parameters managed by the lubricant.
For recirculating lubricant systems, the previous art had taught that when additive concentration levels in sump oil fell below a pre-set trigger, the engine was stopped and the entire lubricating oil was replaced. An improvement on this method allowed for large quantities of the sump oil to be removed and replaced with fresh lubricant during operation. Later practitioners modified this method to extend a recirculating lubricant's useful life by injecting additive into the sump when monitored sump additive concentrations were depleted below a preset level.
The early methods of total or near total lubricant replacement were wasteful because they jettisoned many expensive components if only one additive concentration was lacking. These methods were further deficient in that the concentration of an additive did not necessarily correlate to the actual effectiveness (or ineffectiveness) of the lubricant inside the engine at any given point. Even if it did, substantial research has demonstrated that the concentration of the additive in the sump was not an accurate reflection of the additive concentration at the lubrication point of interest. See Malcolm Fox, et al., “Composition of Lubricating Oil in the Upper Ring Zone of an Internal Combustion Engine”, Tribology International, Vol. 24 No. 4, pp. 231-33 (August 1991). Therefore, these methods were not widely adopted as they did not ensure that the system's actual lubrication needs would be fulfilled.